Roadway repair is often accomplished by overlaying the existing pavement (whether of concrete or asphalt composition) with a new layer (often called a leveling course) of concrete, asphalt or other surfacing materials. Without prior surface treatment, however, this method of repair generally results in the application of insufficient quantities of paving material in the rutted, potholed or otherwise damaged areas, because the overlay will be applied at the same rate per unit of roadway width in damaged areas (which have a greater depth across the width) as in the undamaged areas. The resulting reduced density in the overlay of the previously damaged areas will lead to renewed rutting or other wear damage in the new pavement in relatively short order. However, by milling the surface of the damaged pavement to a uniform surface elevation, the damaged areas will be removed so that newly added pavement will produce a road surface having a consistent elevation across the entire width of the roadway. This repaving technique can be used to return the elevation of a damaged roadway to its original pre-damaged elevation, whereas the placement of a leveling course atop damaged but unmilled pavement will tend to raise the surface of the roadway or some portion thereof above its original elevation. Roadway repair without milling can require the raising of road shoulders, guardrails and manhole covers and the adjustment of overpass clearances, all of which is unnecessary if a proper milling technique is employed. A use of milling prior to repaving can also penult ready establishment of the proper road grade and slope, and thereby avoid drainage and safety problems. Furthermore, milling typically provides a rough surface that readily accepts and bonds with the new asphalt or other pavement overlay. Finally, milling can provide raw material that can be reclaimed for use in the production of new paving materials.
A milling machine is typically a wheeled or track-driven vehicle that is provided with a rotating drum that includes a plurality of cutting teeth. The drum is mounted in a housing on the frame of the machine and adapted to be lowered into contact with the road surface and rotated about a horizontal axis so as to cut into the surface to a desired depth as the machine is advanced along the roadway. Generally, the milling machine also includes a conveyor system that is designed to carry the milled material that has been cut from the roadway by the rotating drum to a location in front of, to the rear of or beside the machine for deposit into a truck for removal from the milling site. One or more spray bars are typically mounted over the conveyors and inside the drum housing so that water may be sprayed to control the dust and heat that is generated in the milling process. In addition, a vacuum system may be provided to assist in removing dust generated in the milling process. Steerable track or wheel drive assemblies are provided to drive the machine and to steer it along a desired milling path. Power for driving the machine and for rotating the drum, either through a belt drive or a hydraulic system, is typically provided by a diesel engine.
Conventional milling machines include one or two front drive assemblies that are generally mounted inside the outer periphery of the machine housing. In addition, such machines usually include two rear drive assemblies, at least one of which extends laterally outside the machine housing to provide a wider footprint for increased stability. These drive assemblies are typically mounted so as to be adjustable in height with respect to the machine frame in order to move the frame carrying the milling drum upwardly and downwardly with respect to the surface on which the milling machine is placed for operation. However, because at least one of the conventional drive assemblies is located laterally outside the machine housing, it is difficult to make a flush cut along the edge of a roadway using such a machine.
It is known to equip a milling machine with an assembly for moving a rear drive assembly between two different positions, a first position which is laterally outside the periphery of the machine housing (and of the milling drum) and a second position which is laterally inside the periphery of the machine housing. Thus, U.S. Pat. No. 6,106,073 describes a milling machine having two rear support wheels, one of which is moveable from an exterior end position that projects beyond the periphery of the housing of the machine to an inside retracted position where the support wheel does not project outside the periphery of the housing. The support wheel moves between the outside and inside positions by a four-bar linkage arrangement that is actuated by a hydraulic cylinder so as to move in a horizontal plane. This machine also includes a separate locking bolt that may be manually placed through locking holes in the frame to retain the rear support wheel in either of the two end positions between which it may be moved.
The four-bar linkage arrangement of the '073 patent is complicated, and the manual locking mechanism is difficult for an operator to engage and disengage. Furthermore, moving a rear support wheel without raising it off the roadway surface requires considerable power, and it stresses the support wheel components.
U.S. Pat. No. 9,068,303 describes a road milling machine having a rear drive unit that is mounted at the lower end of a lifting column. A pivot arm is connected to the lifting column of the rear drive unit and to the machine frame. A steering assembly on the rear drive unit and a controller are provided to steer the rear drive unit while it remains in contact with the roadway and so that it may be operated to drive it between a first position which is laterally outside the machine housing (and of the milling drum) and a second position which is located within a recess of the machine housing. Steering of the rear drive unit while it is in contact with the ground at the first position or the second position in order to begin the process of moving the drive unit puts significant stresses on the steering assembly and the rear drive unit. Furthermore, because the rear drive unit cannot be moved to the second position with its long axis parallel to the side of the machine, the opening in the housing in the second position must be enlarged to permit steering and turning of the rear drive unit therein.
It would be desirable if a simple positioning assembly could be provided that would allow for positioning and locking the drive assembly in an outside position and an inside position without requiring manual manipulation of a locking pin by the operator. It would also be desirable if such a positioning assembly could be provided that would eliminate stress on the drive mechanism caused by maintaining contact with the roadway surface while moving the drive assembly between outside and inside positions. In addition, it would be desirable if the positioning assembly would allow for locking of the drive assembly at one or more intermediate positions between a first position outside the periphery of the housing and a second position inside the periphery of the housing, and for steering of the drive assembly in any position between and including the first position and the second position.